An example of an electromagnetically operated adjusting device for gas exchange valves of this type is shown in DE 30 24 109.
This known device discloses a gas exchange valve for an internal combustion engine, the stem of which is joined to the valve disk and has an anchor plate (or armature) which is alternatingly attracted to the pole surface of two opposing electromagnets upon the energizing the solenoid associated with each electromagnet. The engagement of the anchor plate to a pole surface results in either the closed or open position of the valve. As current flow is cut off to the contacting electromagnet the spring system forces the anchor plate in the direction away from the contacted pole surface where it is then attracted to the opposing pole surface by energization of the solenoid associated with the opposing electromagnet. A disadvantage associated with adjusting devices of this type is the noticeable impact noise of the anchor plate as it contacts each pole surface.
DE 30 24 109 teaches to dampen the impact of the moving anchor plate against the pole surface of an excited electromagnet by providing a biasing member, such as coil spring, to decelerate the anchor plate after it reaches its midpoint of travel prior to impacting the affected pole surface. This method necessitates sturdy coil springs to provide sufficient damping and this means that larger electromagnets are necessary to provide sufficient retention forces for holding the anchor plate at the open and closed positions. Thus, adequate damping results in undesirable increases in the size and weight of the actuator assembly
GB-A 2 137 420 discloses a similar design for an electromagnetically-operated, spring-biased adjusting device wherein damping of the anchor plate impact is achieved by providing a skirt-like sealing member to the pole surface of each electromagnet whereby an enclosed volume of air is formed by the electromagnet pole surface and the skirt-like sealing member just before the anchor plate impacts the pole surface. This volume of air cushions the impact as it becomes compressed and impact noise is reduced. However, since only the last portion of anchor plate travel is controlled by this sealing affect, the ability to adequately control the impact damping of a fast approaching anchor plate is limited by the cushioning effect attributed to this small volume which is sealed only just prior to impact.
Thus, there is a definite need in the art for an improved solenoid actuated, spring-biased, adjusting device for gas exchange valves which has improved means for significantly damping the impact noise associated with the anchor plate and which also allows for fast switching time behavior.